The present invention relates to a gripping device, and more specifically, but not exclusively, to a gripping device intended for gripping bottles or like objects and being of the kind which includes a gripping block in which there is embodied a plurality of through-passing cylindrical channels in each of which there is disposed a gripping element in the form of a support sleeve which has mounted thereon a substantially cylindrical muff made of an elastic material, and air passages which are operative in delivering air under pressure to the space located between the muff and the support sleeve, such as to deform the muff.
Such gripping devices may, for instance, be incorporated in machines for lifting return bottles from crates arriving at a brewery and for placing filled bottles into crates to be distributed from a brewery. Normally, a plurality of bottle-gripping devices, corresponding in number to the number of bottles in a crate, are mutually coupled to form a co-acting unit. In those instances when it is likely that the distances between adjacent rows of bottles in a crate or on the bottle conveyer belt will vary, the grippers may be constructed for mutual displacement in relation to one another, so that the grippers can be brought into their correct position.
Bottle grippers of this known kind, with which respective bottles are gripped with the aid of an elastic muff, preferably a rubber muff disposed in an air passage, afford certain advantages over those bottle grippers with which the bottles are gripped with the aid of balls or like elements urged into engagement with the bottle head.
DE-A1-2 845 094 teaches a bottle gripping device which includes a rubber muff arranged in a through-passing channel for co-action with a bottle head. In this case, however, the rubber muff is mounted between the support sleeve and a screw-threaded plug. Thus, the attachment is achieved solely by the clamping action obtained between the plug and the support sleeve, and has been found unreliable in practice. Among other things, it is difficult in this way to achieve a positive attachment capable of withstanding high pressure impacts.
A more serious drawback with this prior art attachment is that the muff anchorage is progressively impaired, even in normal use of the gripper, and finally results in a gripper which will no longer function in the manner intended. This is due to the fact that when the rubber muff is deformed, creep occurs in the rubber material beyond the position at which the muff is clamped. When the pressure is subsequently equalized, the elasticity of the rubber material is not sufficient to retract the rubber material past the clamping location. Consequently, material migrates progressively beyond said clamping location.
U.S. Pat. No. 4,486,045 teaches a gripping device with which this problem is alleviated, by arranging and configuring the rubber muffs in a manner such that the muffs are self-locking in the channels as a result of the elevated air pressure acting on respective muffs, this elevated pressure also increasing the frictional force between the muff and the channel wall, so that the muff retaining force will increase with increasing pressure.
In order, inter alia, to prevent the sleeve and the muff from being pressed up through the channel when a holder means forming part of the grip arrangement is lowered over a bottle, a screw-threaded plug having a through-passing bore whose diameter is smaller than the diameter of the channel is screwed into the holder means so as to hold the gripping device in position.
Although this known gripping arrangement functions quite satisfactorily in practice, the task of replacing defective rubber muffs is relatively laborious and difficult to carry out, particularly in those instances when the gripping device is so mounted as to leave only a very small space above the gripper elements. This lack of space makes it difficult to unscrew respective plugs so as to enable a defective muff to be removed and replaced with a new muff. It will be understood that it is imperative with machines of this kind that stationary periods can be reduced to a minimum in the event of a malfunction. Furthermore, the construction of the known gripping device is unnecessarily complicated, since it includes a multiplicity of elements or components.